Fixed a formating issue...

Attached patch is for Bug 13217 - "thread apply all detach throws a 
SEGFAULT".

Issue:
Segmentation fault was coming from invalid access to tp->* i.e "tp->ptid".

Fix:
Check if the thread is valid before we apply a command
Check for the thread count after executing a command on every thread

Testing:
* Tested on powerpc-linux as well as i686-pc-linux
* Also checked with valgrind

Test case:
Added a test case to test "thread apply all detach" command

Regards,
-Ali